This invention relates to a portable radio communication unit, and it relates more particularly to such a unit with an antenna substantially within the profile of such unit. The term "radio communication unit" includes, for example, a radio paging unit, a cordless telephone handset that is normally useful with only a single base station having an assigned directory number, and a readily transportable radiotelephone transceiver that has its own directory number and is normally useful with any base station to which it may be close. The invention is considered herein, for convenience and without limit intended, in relation to a hand-held portable radiotelephone unit.
There have been a number of efforts in the past to provide an antenna inside a portable radio communication unit for at least the purpose of signal reception and in some cases for signal transmission as well. Such efforts have sought at least to reduce the need to have an external rod or whip antenna because of the inconveniences of handling and carrying such a unit with the external antenna extended. This has even been true of portable radiotelephone units operating in relatively high frequency ranges such as those of the cellular radiotelephone systems where a suitable rod antenna may be about six inches long.
Microstrip-type antennas have been known in the art for applications in which a thin antenna was required, and such antennas have been devised in which the antenna could be made to conform to a curved surface such as the surface of an aircraft or a missile. Such an antenna is shown in the U.S. Pat. Nos. 4,078,237 and 4,095,277 to C. M. Kaloi. However, these antenna systems usually include a ground plane member of at least one wavelength in dimension beyond each edge of the associated radiator element. The need for such a large antenna component makes these antennas unsuitable for use as an antenna in a portable radiotelephone unit that operates in, e.g., the 900 megahertz (MHz) frequency spectrum region and that should have a hand-held level of portability.
Efforts to provide an antenna, or otherwise eliminate the need for a protruding antenna, have included various contrivances. One example is shown in the U.S. Pat. No. 3,736,591 to L. W. Rennels et al. where selected conductive walls of an equipment housing are employed as part of a loop antenna for reception, but one portion is extended for transmission. The U.S. Pat. No. 4,723,305 to J. P. Phillips et al. illustrates an example in which a notch antenna is formed as a part of, and dividing the internal volume of, a conductive equipment housing in a portable radiotelephone unit. Yet another example, U.S. Pat. No. 4,641,366 to Y. Yokoyama et al., shows a portable radiotelephone unit having dual-band capability and in which a conductive casing has a recessed surface to which two, side-by-side, radiating plate antennas are electrically connected to form, with the conductive casing, a dual-band antenna system. These efforts usually have involved either substantial intrusions into the limited space available for housing transmitter/receiver electronic apparatus or substantial complexity, either or both of which factors render manufacturing difficult and costly.